geekdoc-python-zh/docs/py4b/python-list-manipulation.md

Python 中的列表操作

原文：https://www.pythonforbeginners.com/basics/python-list-manipulation

概观

List 是 Python 中最简单也是最重要的数据结构之一。

列表用方括号[ ]括起来，每个项目用逗号分隔。

列表是项目的集合，其中列表中的每个项目都有一个分配的索引值。

列表是可变的，意味着你可以改变它的内容。

列表非常灵活，有许多内置的控制功能。

列表对象的方法

对列表方法的调用使它们操作的列表出现在方法名之前，用点分隔，例如 L.reverse()

 Creation
L = ['yellow', 'red', 'blue', 'green', 'black']
>>>print L
returns: ['yellow', 'red', 'blue', 'green', 'black']

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Accessing / Indexing
L[0]  = returns 'yellow'

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Slicing
L[1:4]  = returns ['red', 'blue', 'green']
L[2:] 	= returns ['blue', 'green', 'black']
L[:2] 	= returns ['yellow', 'red']
L[-1]  	= returns 'black'
L[1:-1] = returns ['red', 'blue', 'green']

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Length - number of items in list
len(L)  = returns 5

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Sorting - sorting the list
sorted(L) = returns ['black', 'blue', 'green', 'red', 'yellow']

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Append - append to end of list
L.append("pink")

>>> print L
returns: ['black', 'blue', 'green', 'red', 'yellow', 'pink']

##########

Insert - insert into list
L.insert(0, "white")

>>> print L
returns: ['white', 'black', 'blue', 'green', 'red', 'yellow', 'pink']

##########

Extend - grow list

L.extend(L2)

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Remove - remove first item in list with value "white"

L.remove("white")

>>> print L
returns: ['black', 'blue', 'green', 'red', 'yellow', 'pink']

##########

Delete

Remove an item from a list given its index instead of its value
del.L[0]

>>> print L
['blue', 'green', 'red', 'yellow', 'pink']

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Pop

Remove last item in the list
L.pop()  = returns 'pink'

# remove indexed value from list
L.pop(1) = returns 'green'  

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Reverse - reversing the list
L.reverse()

##########

Count

Search list and return number of instances found
L.count('red')

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Keyword "in" - can be used to test if an item is in a list

if 'red' in L:
    print "list contains", 'red'

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For-in statement - makes it easy to loop over the items in a list
for item in L:
    print item

L = ['red', 'blue', 'green']
for col in L:
    print col